1. Field of the Disclosure
This invention relates to the field of laser safety systems and, in particular, a method is described for electronically bringing a high power fiber laser to a safe state by means of functions which are integrated into the power source of the laser.
2. Prior Art
High power lasers with semiconductor pumping, for example fiber lasers, are widely used for processing various materials. Powerful laser radiation is hazardous for humans when various human organs, especially the eyes, are directly exposed to the laser radiation. Therefore, the system integrators should provide safety measures for protecting the personnel who work in the vicinity of operating high power lasers. These measures are generally related to constructing a closed protective booth around the workpiece to be laser processed. The booth keeps the laser radiation from penetrating beyond its boundaries and may be accessed, for example, to change the workpiece or for other purposes. Clearly, when the booth is accessed, it is necessary to bring the laser to a safe state/regime in which no laser radiation is generated.
Typically, the laser itself is located outside the protective booth with the laser radiation being guided into the booth by a delivery fiber. In the latter configuration, it is necessary to monitor the integrity of the laser itself and that of the delivery fiber in order to bring the laser to the safe regime once a need arises.
The safety measures require that the laser's developer provide the system integrator with the possibility (interface) of bringing the laser to a safe state in which it is not possible to generate laser radiation. The current machine safety standards, such as ISO 13849-1, define safety system categories (Performance Levels) depending on the probability of failure of the safety system in response to a single or multiple faults. The current minimum for the safety systems of powerful lasers is Cat. 3 PLD according to ISO 13849-1 requiring that a single fault of safety system should not lead to the loss of the safety function, and whenever reasonably practical, the single fault shall be detected at or before the next demand upon the safety function is received.
One of the current widespread methods for bringing not only lasers, but also other electrical machines to a safe state includes disconnecting (de-energizing) them from the power grid with the help of two redundant contactors connected in series and controlled with the help of a safety relay which also monitors their status in the work process. An example of this system is shown in FIG. 1. When the contactors are open, the laser is disconnected from an energy source. If there are capacitances in the system capable of storing sufficient energy to generate hazardous radiation, they must be discharged so as to bring the laser to the safe state. The discharge can be forced by means of auxiliary, normally closed contacts of contactors. Such as solution has shortcomings for applications where it is necessary to rapidly and frequently bring the laser to a safe regime, such as on processing conveyor lines, where the processing cycle lasts no longer than several seconds. In this case, the mechanical lifetime of the contactors is exhausted very quickly, which leads to their frequent replacement. Furthermore, every time the contactors are switched to the closed position, a laser system “cold” starts which takes a relatively long time in order to get the system ready for work. This leads to expensive delays in the operation of conveyor lines.
An alternative solution providing the required safety measures includes the installation of a special shutter (optical safety shutter) in the path of the laser radiation. However, in the case of a fiber laser or another type of laser with a radiation delivery fiber, this arrangement inevitably requires that the radiation be emitted from the fiber and subsequently reverse inputted into the fiber, which degrades the quality (brightness) of this radiation and negatively affects the reliability of the entire system. Furthermore, such an arrangement considerably raises the price of the system.